How did Montana get its shape?
Montana was originally cut from the existing boundaries of the Idaho Territory. Congress kept the Idaho Territory’s northern and eastern borders as they were, flat and straight.
They drew the southern border along the 45th parallel to 111° W, turned south to the Bitterroot Range, followed the Bitterroots up to the 116° line, and followed this (the straight vertical section in the northwest corner of MT) to the British possessions (Canada).
Read on for the condensed story of how it all came to be.
How Montana got its borders (condensed history)
Table of Contents:
- General outline
- Drawing the north border
- Drawing the west border
- Drawing the east border
- Drawing the south border
In 1862, prospectors struck gold in Bannack, present-day southwestern Montana, and miners started flocking to this region of the country in the thousands. Within no time, they were pressing Congress to establish their own territory.
Congress obliged and the Idaho Territory was created in 1863, encompassing all of present-day Idaho and Montana and most of Wyoming.
With its administrative center in Lewiston, on the far eastern border of the territory, it proved difficult to govern the entire territory, half of which lay across the jagged Rocky Mountains that cut through its center.
To appease the local miners east of the Rocky Mountains, in 1864, Congress decided to cut Montana Territory from the Idaho Territory, creating the present-day borders of Montana. However, it took several rough drafts before they settled on the state’s final shape.
General outline
Congress decided that the Montana Territory would occupy the northeastern third of the Idaho Territory, from the Continental Divide to the Dakota Territory in the east, and to the British possessions in the north (present-day Canada).
Drawing the north border
The north border remained as it was – the 49th Parallel separating Canada from the United States.
Drawing the west border
Congress decided the west border of Montana would follow the peaks of the Bitterroot Range from the southwest corner up to the 116° W line, which it then followed north to the British possessions (Canada).
This explains why the border between Montana and Idaho is not straight.
An initial proposal had the border along the Continental Divide, roughly 130 miles (209 km) east of where it lies today, but a later push from Idaho Chief Justice Judge Sidney Edgerton shifted the border west, following the peaks of the Rocky Mountains instead.
Drawing the east border
To create the east border of Montana, Congress simply extended the Idaho Territory’s existing eastern border down to the 45th parallel. From there, it turned west to establish the south border, which took some time to finalize.
Drawing the south border
Initially, Congress considered the following proposal for Montana’s southern border:
Follow the 45th parallel (the bottom of Montana’s east border) west to 111° W, turn south one-half a degree, then turn west to meet the Idaho border on the Continental Divide in the Bitterroot Mountains.
This created a small point out of the Dakota Territories sticking in between Montana and Idaho. It also created a square shape south of Montana and made an odd, impractical shape out of the Dakota Territories (see above draft).
Congress then decided to establish Wyoming from the square shape below Montana. To do this, they continued Montana’s eastern border down to Colorado, turned west along the 41st parallel to 111° W, and followed 111° W north to the Montana border (green dashed line in the above draft).
This left a small exclave of the Dakota Territory in between Wyoming, Idaho, and Montana, about where present-day West Yellowstone is located, called Lost Dakota.
Unimpacted by the newly-drawn boundary lines, this wild, uninhabited exclave remained a part of the Dakota Territory until it was given to Montana in 1873.
And thus, the jagged western border of Montana with its southwestern dip was established:
Over the following 25 years, Montana Territory’s population and economy grew, and in 1889, President Benjamin Harrison proclaimed Montana the 41st state of the union.
Montana’s borders haven’t changed since then.
How did Montana become a state?
Find out how the Idaho Territory first came to be, and why they decided to carve Montana from it in our article, Montana’s Winding Path to Statehood [CONDENSED HISTORY].
FAQs about Montana’s border
Why is the border between Montana and Idaho not straight?
When Congress created the Montana Territory in 1864, it decided to run the border between Montana and Idaho along the peaks of the Bitterroot Mountains, from the southwest point where Montana, Wyoming, and Idaho met, up to the British possessions (Canada) in the northwest.
What divides Montana and Idaho?
The Bitterroot Range in southwestern Montana divides Montana and Idaho, serving as the official state border.
How many borders does Montana have?
Montana has four borders. Montana shares its eastern border with North and South Dakota, its southern border with Wyoming, its western border with Idaho, and its northern border with Canada.
